The present invention relates to anti-fungal/anti-parasitic agents, in particular, derivatives of Echinocandin compounds and their use in the treatment of fungal and parasitic infections.
A number of naturally occurring cyclic peptides are known in the art including echinocandin B (A30912A), aculeacin, mulundocandin, sporiofungin, L-671,329, and S31794/F1. In general, these cyclic peptides may be structurally characterized as a cyclic hexapeptide core (or nucleus) with an acylated amino group on one of the core amino acids. This acyl group is typically a fatty acid moiety forming a side chain off the nucleus. For example, echinocandin B has a linoleoyl side chain while aculeacin has a palmitoyl side chain.
These natural products have limited inherent antifungal and antiparasitic.properties. The natural compounds may be structurally modified in order to enhance these properties or to improve the compound""s stability and/or water solubility. Turner, W. W., Rodriguez, M. J., Cur. Pharm. Des., 2:209, 1996. For example, the fatty acid side chain may be removed from the cyclic peptide core to provide an amino nucleus which may then be re-acylated to provide semi-synthetic compounds. Furthermore, the homotyrosine moiety in the cyclic peptide may be O-glycosylated to provide further elaborated, novel, semi-synthetic compounds such as those claimed in the present application.
This invention relates to compounds of formula I: 
where:
R is independently at each occurrence hydrogen, hydroxy, or Oxe2x80x94Pg;
R1 is hydrogen, methyl, CH2C(O)NH2, CH2C(O)NHxe2x80x94Pg;
R2 and R3 are independently hydrogen or methyl;
R4 is a moiety of the formula: 
R5 is a moiety of the formula: 
A is independently at each occurrence phen-di-yl, pyridin-di-yl, pyridazin-di-yl, pyrimidin-di-yl, pyrazin-di-yl, furan-di-yl, or thiophen-di-yl rings;
X is independently at each occurrence a bond or Cxe2x89xa1C;
R6 is hydrogen, C1-C12 alkyl, C2-C12 alkynyl, C1-C12 alkoxy, C1-C12 alkylthio, halo, or xe2x80x94Oxe2x80x94(CH2)mxe2x80x94[Oxe2x80x94(CH2)n]pxe2x80x94Oxe2x80x94(C1-C12 alkyl), or xe2x80x94Oxe2x80x94(CH2)qxe2x80x94Zxe2x80x94R8;
R7 is independently at each occurrence hydrogen, hydroxy, amino, azido, OR5, Oxe2x80x94Pg, or NHpxe2x80x94Pg;
R7xe2x80x2 is CHR7CH2R7, CHR7CH2OR9, ethyl, CHR7CO2H, CHR7CH2Oxe2x80x94Pg, or CHR7C(O)xe2x80x94Pg;
R7xe2x80x3 is hydrogen, CH2R7, CH2O R9, methyl, CO2H, CH2Oxe2x80x94Pg, CH2NHpxe2x80x94Pg, or C(O)xe2x80x94Pg;
m, n, and q are independently 2, 3 or 4;
p is 0 or 1;
Z is pyrrolidin-di-yl, piperidin-di-yl, or piperazin-di-yl;
R8 is hydrogen, C1-C12 alkyl, benzyl, or methyl(C3-C12 cycloalkyl);
R9 is SO3H or a moiety of the formula: 
R10 is hydroxy, C1-C6 alkyl, C1-C6 alkoxy, phenyl, phenoxy, p-halophenyl, p-halophenoxy, p-nitrophenyl, p-nitrophenoxy, benzyl, benzyloxy, p-halobenzyl, p-halobenzyloxy, p-nitrobenzyl, or p-nitrobenzyloxy; and
Pg is a hydroxy, amino, amido or carboxy protecting group; with the proviso that the total number of R7 substituents that are OR5 groups does not exceed two; or a pharmaceutical salt or solvate thereof,
which are useful as antifungal and antiparasitic agents or intermediates to such agents.
Furthermore, the present invention relates to pharmaceutical formulations comprising one or more pharmaceutical carriers, diluents or excipients and a compound of formula I.
Moreover, the present invention relates to methods for inhibiting fungal and parasitic activity comprising administering an effective amount of a compound of formula I to a host in need of such treatment.
The Compounds:
As used herein, the term xe2x80x9cC1-C12 alkylxe2x80x9d refers to a straight or branched saturated alkyl chain having from one to twelve carbon atoms. Typical C1-C12 alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, t-butyl, pentyl, 5-methylpentyl, hexyl, heptyl, 3,3-dimethylheptyl, octyl, 2-methyl-octyl, nonyl, decyl, undecyl, dodecyl and the like. The term xe2x80x9cC1-C12 alkylxe2x80x9d includes within its definition the terms xe2x80x9cC1-C16 alkylxe2x80x9d, xe2x80x9cC1-C4 alkylxe2x80x9d, and xe2x80x9cC3-C12 cycloalkylxe2x80x9d. The term xe2x80x9cC3-C12 cycloalkylxe2x80x9d refers to a cyclic saturated alkyl chain having from 3 to 12 carbon atoms. Moreover, the term xe2x80x9cC3-C12 cycloalkylxe2x80x9d includes within its definition the term xe2x80x9cC3-C7 cycloalkylxe2x80x9d.
The term xe2x80x9cC2-C12 alkynylxe2x80x9d refers to a straight or branched mono-alkynyl chain having from two to twelve carbon atoms. Typical C2-C12 alkynyl groups include ethynyl, 1-propyn-1-yl, 1-propyn-2-yl, 1-butyn-1-yl, 1-butyn-3-yl, 1-pentyn-3-yl, 4-pentyn-2-yl, 1-hexyn-3-yl, 3-hexyn-1-yl, 5-methyl-3-hexyn-1-yl, 5-octyn-1-yl, 7-octyn-1-yl, 4-decyn-1-yl, 6-decyn-1-yl and the like.
The term xe2x80x9chaloxe2x80x9d refers to chloro, fluoro, bromo or iodo.
The term xe2x80x9cC1-C12 alkoxylxe2x80x9d refers to a C1-C12 alkyl group attached through an oxygen atom. Typical C1-C12 alkoxy groups include methoxy, ethoxy, propoxy, butoxy, sec-butoxy, n-pentoxy, 5-methyl-hexoxy, heptoxy, octyloxy, decyloxy dodecyloxy and the like. The term xe2x80x9cC1-C12 alkoxyxe2x80x9d includes within its definition the terms xe2x80x9cC1-C6 alkoxyxe2x80x9d, xe2x80x9cC3-C7 alkoxyxe2x80x9d, and xe2x80x9cC1-C4 alkoxyxe2x80x9d.
The term xe2x80x9cC1-C12 alkylthioxe2x80x9d refers to a C1-C12 alkyl group attached through a sulfur atom. Typical C1-C12 alkylthio groups include methylthio, ethylthio, propylthio, isopropylthio, butylthio, 3-methyl-heptylthio, octylthio, 5,5-dimethyl-hexylthio and the like. The term xe2x80x9cC1-C12 alkylthioxe2x80x9d includes within its definition the terms xe2x80x9cC1-C6 alkylthioxe2x80x9d and xe2x80x9cC1-C4 alkylthioxe2x80x9d.
The symbol xe2x80x9cOxe2x80x94Pgxe2x80x9d and term xe2x80x9chydroxy protecting groupxe2x80x9d refer to a substituent of a hydroxy group that is commonly employed to block or protect the hydroxy functionality while reactions are carried out on other functional groups on the compound. This substituent, when taken with the oxygen to which it is attached, may form an ether, e.g., methyl, methoxymethyl, and benzyloxymethyl ether, a silyl ether, an ester, e.g. acetoxy, or a sulfonate moiety, e.g. methane and p-toluenesulfonate. The exact genus and species of hydroxy protecting group is not critical so long as the derivatized hydroxy group is stable to the conditions of subsequent reaction(s) and can be removed at the appropriate point without disrupting the remainder of the molecule. A preferred hydroxy protecting group is acetyl. Specific examples of hydroxy protecting groups are described in T. W. Greene, xe2x80x9cProtective Groups in Organic Synthesis,xe2x80x9d John Wiley and Sons, New York, N.Y., (2nd ed., 1991), (hereafter referred to as Greene) chapters 2 and 3 and in the Preparations and Examples section which follows.
The symbol xe2x80x9cNHpxe2x80x94Pgxe2x80x9d and term xe2x80x9camino protecting groupxe2x80x9d as used in the specification refer to a substituent of the amino group commonly employed to block or protect the amino functionality while reacting other functional groups on the compound. When p is 0, the amino protecting group, when taken with the nitrogen to which it is attached, forms a cyclic imide, e.g., phthalimido and tetrachlorophthalimido. When p is 1, the protecting group, when taken with the nitrogen to which it is attached, can form a carbamate, e.g., methyl, ethyl, and 9-fluorenylmethylcarbamate; or an amide, e.g., N-formyl and N-acetylamide. The exact genus and species of amino protecting group employed is not critical so long as the derivatized amino group is stable to the condition of subsequent reaction(s) on other positions of the intermediate molecule and can be selectively removed at the appropriate point without disrupting the remainder of the molecule including any other amino protecting group(s). Preferred amino protecting groups are t-butoxycarbonyl (t-Boc), allyloxycarbonyl, phthalimido, and benzyloxycarbonyl (CbZ). Further examples of groups referred to by the above terms are described in Greene at chapter 7.
The symbol C(O)xe2x80x94Pg and the term xe2x80x9ccarboxy protecting groupxe2x80x9d refer to a substituent of a carbonyl that is commonly employed to block or protect the carboxy functionality while reactions are carried out on other functional groups on the compound. This substituent, when taken with the carbonyl to which it is attached, may form an ester, e.g., C1-C6 alkyl, substituted C1-C6 alkyl, C2-C6 alkenyl, substituted C2-C6 alkenyl, benzyl, substituted benzyl, benzhydryl, substituted benzhydryl, trityl, substituted trityl, and trialkylsilyl ester. The exact species of carboxy protecting group is not critical so long as the derivatized carboxy group is stable to the conditions of subsequent reaction(s) and can be removed at the appropriate point without disrupting the remainder of the molecule. Other examples of groups referred to by the above terms are described in Greene, at chapter 5.
The symbol xe2x80x9cC(O)NHxe2x80x94Pgxe2x80x9d and term xe2x80x9camido protecting groupxe2x80x9d as used in the specification refer to a substituent of an amide commonly employed to block or protect the amino portion while reacting other functional groups on the compound. This protecting group, when taken with the nitrogen to which it is attached, may form an amide, e.g. N-allyl, N-methoxymethyl, and N-benzyloxymethyl amide. The exact species of amido protecting group employed is not critical so long as the derivatized amido group is stable to the condition of subsequent reaction(s) on other positions of the intermediate molecule and can be selectively removed at the appropriate point without disrupting the remainder of the molecule including any other amido protecting group(s). Other examples of groups referred to by the above terms are described in Greene, at chapter 7, pg. 397.
The term xe2x80x9cpharmaceutical saltxe2x80x9d as used herein, refers to salts of the compounds of formula I which, at the doses administered, are substantially non-toxic to living organisms. Typical pharmaceutical salts include those prepared by reaction of the compounds of the present invention with a mineral or organic acid or inorganic base. Such salts are known as acid addition and base addition salts. For further exemplification of pharmaceutical salts, see e.g. Berge, S. M, Bighley, L. D., and Monkhouse, D. C., J. Pharm. Sci., 66, 1, 1977.
The term xe2x80x9csolvatexe2x80x9d represents an aggregate that comprises one or more molecules of the solute, such as a formula I compound, with one or more molecules of solvent.
Reagents:
The term xe2x80x9csuitable solventxe2x80x9d refers to any solvent, or mixture of solvents, inert to the ongoing reaction that sufficiently solubilizes the reactants to afford a medium within which to effect the desired reaction.
The term xe2x80x9cthermodynamic basexe2x80x9d refers to a base which provides a reversible deprotonation of an acidic substrate or is a proton trap for those protons that may be produced as byproducts of a given reaction, and is reactive enough to effect the desired reaction without significantly effecting any undesired reactions. Examples of thermodynamic bases include, but are not limited to, acetates, acetate dihydrates, carbonates, bicarbonates, C1-C4 alkoxides, and hydroxides (e.g. lithium, sodium, or potassium acetate, acetate dihydrate, carbonate, bicarbonate, methoxide, or hydroxide), tri-(C1-C4 alkyl)amines, or aromatic nitrogen containing heterocycles (e.g. imidazole and pyridine).
The Methods:
The term xe2x80x9cinhibitingxe2x80x9d includes prohibiting, stopping, retarding, alleviating, ameliorating, halting, restraining, slowing or reversing the progression, or reducing the severity of the growth or any attending characteristics, symptoms, and results from the existence of a parasite or fungus. As such, these methods include both medical therapeutic (acute) and/or prophylactic (prevention) administration as appropriate.
The term xe2x80x9ceffective amount,xe2x80x9d means an amount of a compound of formula I which is capable of inhibiting fungal and/or parasitic activity.
Compounds:
Preferred compounds of this invention are those compounds of formula I where:
R is hydroxy at each occurrence;
R1, R2, and R3 are each methyl; and
R4 is a moiety of the formula: 
a pharmaceutical salt or solvate thereof.
Of these compounds, more preferred are those compounds of formula I where:
R4 is a moiety of the formula: 
R5 is a moiety of the formula: 
R6 is hydrogen or C3-C7 alkoxy;
R7 is independently at each occurrence hydrogen, hydroxy, amino, or OR5; and
R7xe2x80x3 is hydrogen, CH2R7, CH2OR9, methyl, CO2H, or C(O)xe2x80x94Pg; or a pharmaceutical salt or solvate thereof.
Of these compounds, further preferred are those compounds of formula I where:
R6 is n-pentoxy;
R7 is independently at each occurrence hydroxy or amino;
R7xe2x80x3 is hydrogen, hydroxymethyl, CH2OR9, methyl, or CO2Me; and
R9 is a moiety of the formula: 
or a pharmaceutical salt thereof.
Of these compounds even more preferred are those compounds of formula 1 where:
R7 is independently at each occurrence hydroxy;
R10 is C1-C4 alkyl; or a pharmaceutical salt thereof.
Preferred pharmaceutical acid addition salts are those formed with mineral acids such as hydrochloric acid and sulfuric acid, and those formed with organic acids such as maleic acid, tartaric acid, and methanesulfonic acid.
Preferred pharmaceutical base addition salts are the potassium and sodium salt forms.
Methods:
Preferred methods include inhibiting fungal activity arising from Candida albicans, Aspergillus fumigatis, and Candida parapsilosis and inhibiting parasitic activity arising from Pneumocystis carinii. 
The compounds of formula I may be prepared from compounds of formula II(d) as illustrated in Scheme 1 below where R, R1, R2, R3, R4, and R5 are as defined above. 
A compound of formula II(d) may be O-glycosylated by procedures known in the art to form a compound of formula I(a). See e.g., Toshima, K., and Tatsuta, K., xe2x80x9cRecent Progress in O-Glycosylation Methods and Its Application to Natural Products Synthesis,xe2x80x9d Chem. Rev., 93:1503, 1993. For example, a protected mono, di, or trisaccharide of formula III or IV may be added to a compound of formula II(d), dissolved or suspended in a suitable solvent, in the presence of a suitable thermodynamic base and suitable activating reagent. Such a procedure is a well known variant of the xe2x80x9cKoenigs and Knorr Reactionxe2x80x9d. Id. A convenient and preferred solvent for this procedure is an aprotic solvent such as tetrahydrofuran. A convenient and preferred thermodynamic base is silver carbonate. Suitable activating reagents include, but are not limited to, silver trifluoromethanesulfonate, silver(I) oxide, silver carbonate, silver perchlorate, silver nitrate, silver silicate, mercury(II) cyanide, bromide, chloride, and iodide, mixtures thereof, and the like. A convenient and preferred activating reagent is silver trifluoromethanesulfonate. See Example 1 below for further instruction on reaction conditions.
The compounds of formula I, where any of R7, R7xe2x80x2, or R7xe2x80x3 are amino may be formed from the compounds of formula I where R7, R7xe2x80x2, or R7xe2x80x3 are azido as described in Example 41 below or by analogous procedures well known in the art. See, e.g., Larock, xe2x80x9cComprehensive Organic Transformations,xe2x80x9d pg. 409, VCH Publishers, New York, N.Y., 1989.
The compounds of formula I where R7xe2x80x2 or R7xe2x80x3 is CHR7CH2OH or hydroxymethyl respectively may be phosphorylated or phosphonylated by reaction with an appropriately substituted dichloro-phosphate or phosphonic acid of formula V: 
in the presence of a suitable base to provide, following an aqueous workup, a compound of formula I where R9 is a moiety of the formula: 
Suitable bases include lithium trimethylsilanolate (LiOTMS), and lithium bis(trimethylsilyl)amide (LHMDS). A convenient and preferred solvent is an aprotic solvent such as tetrahydrofuran and/or dimethylformamide.
Alternatively, the compounds of formula I where R7xe2x80x2 or R7xe2x80x3 is CHR7CH2OH or hydroxymethyl respectively may be sulfated by reaction with a suitable sulfation reagent by the procedures taught in Guiseley and Ruoff, J. Org. Chem., 26:1248, 1961.
The protected compound of formula I(a) may optionally have its protecting group(s) removed to form a compound of formula I. Initial choices of protecting groups, and methods for their removal, are well known in the art. See, e.g., Greene cited above. Preferred choices and methods may be found in the Examples section which follows, e.g., Example 40.
The pharmaceutical salts of the invention are typically formed by reacting a compound of formula I(a) or I with an equimolar or excess amount of acid or base. The reactants are generally combined in a mutual solvent such as diethylether, tetrahydrofuran, methanol, ethanol, isopropanol, benzene, and the like for acid addition salts, or water, an alcohol or a chlorinated solvent such as methylene chloride for base addition salts. The salts normally precipitate out of solution within about one hour to about ten days and can be isolated by filtration or other conventional methods.
Acids commonly employed to form acid addition salts are inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, phosphoric acid, and the like, and organic acids such as p-toluenesulfonic, methanesulfonic acid, ethanesulfonic acid, oxalic acid, p-bromophenylsulfonic acid, carbonic acid, succinic acid, citric acid, tartaric acid, benzoic acid, acetic acid, and the like.
Base addition salts include those derived from inorganic bases, such as ammonium or alkali or alkaline earth metal hydroxides, carbonates, bicarbonates, and the like. Such bases useful in preparing the salts of this invention thus include sodium hydroxide, potassium hydroxide, ammonium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, calcium hydroxide, calcium carbonate, and the like.
It should be recognized that the particular counterion forming a part of any salt of this invention is not of a critical nature, so long as the salt as a whole is pharmacologically acceptable and as long as the counterion does not contribute undesired qualities to the salt as a whole.
Compounds of formula I(d) may be prepared as illustrated in Scheme 2 below where Rnat is a side chain found on a naturally occurring cyclic peptide described above, R11 and R11xe2x80x2 are independently hydrogen or hydroxy, and R, R1, R2, R3, R4, and R5 are as defined above 
A naturally occurring cyclic peptide of formula II(a) may be deacylated using procedures known in the art to provide an amino nucleus of formula II(b). This reaction is typically carried out enzymatically by exposing the naturally occurring cyclic peptide to a deacylase enzyme. The deacylase enzyme may be obtained from the microorganism Actinoplanes utahensis and used substantially as described in U.S. Pat. Nos. 4,293,482 and 4,304,716, the teachings of each are herein incorporated by reference. The deacylase enzyme may also be obtained from the Pseudomonas species. Deacylation may be accomplished using whole cells of Actinoplanes utahensis or Pseudomonas or the crude or purified enzyme thereof or using an immobilized form of the enzyme. See European Patent Application No. 0 460 882 (Dec. 11, 1991). Examples of naturally occurring cyclic peptides which may be used as starting materials include aculeacin (palmitoyl side chain), tetrahydroechinocandin B (stearoyl side chain), mulundocandin (branched C15 side chain), L-671,329 (C16 branched side chain), S 31794/F1 (tetradecanoyl side chain), sporiofungin (C15 branched side chain), FR901379 (palmitoyl side chain) and the like. A preferred naturally occurring cyclic peptide is echinocandin B (a compound of formula II(a) where R1, R2 and R3 are each methyl, R, R11, and R11xe2x80x2 are hydroxy at each occurrence, and Rnat is linoleoyl).
The amino nucleus of formula II(b) may be re-acylated, and the hydroxy groups when present at R11 and/or R11xe2x80x2 removed (deoxygenated), by procedures taught in U.S. Pat. Nos. 5,646,111, and 5,693,611, the teachings of each are herein incorporated by reference, to provide the compounds of formula II(d). See Preparation 11 and 12 below for an example of these two transformations.
The cyclic peptides of formula II(a) may be prepared by fermentation of known microorganisms. For example, the cyclic peptide of formula II(a) where R1, R2 and R3 are methyl, R, R11, and R11xe2x80x2 are hydroxy at each occurrence (cyclic nucleus corresponding to A-30912A) may be prepared using the procedure detailed in Abbott, et al., U.S. Pat. No. 4,293,482, the teachings of which are herein incorporated by reference. The cyclic peptide of formula II(a) where R1, R2 and R3 are methyl, R11 is hydroxy, R11xe2x80x2 is hydrogen, and R is hydroxy at each occurrence (cyclic nucleus corresponding to A-30912B) may be prepared using the procedure detailed in Abbott, et al., U.S. Pat. No. 4,299,763, the teachings of which are herein incorporated by reference. Aculeacin may be prepared using the procedure detailed in Mizuno, et al., U.S. Pat. No. 3,978,210, the teachings of which are herein incorporated by reference. The cyclic peptide of formula II(a) where R1 is CH2C(O)NH2, R2 is methyl, R3 is hydrogen, and R, R11, and R11xe2x80x2 are hydroxy at each occurrence may be prepared by deacylating the cyclic peptide prepared using the procedure detailed in Chen, et al., U.S. Pat. No. 5,198,421, the teachings of which are herein incorporated by reference. Furthermore, cyclic peptides of formula II(d) where R4 contains 1 or more heterocyclic rings may be prepared as taught in U.S. Pat. No. 5,693,611, the teachings of which are herein incorporated by reference.
Compounds of formula III, IV, and V are known in the art and to the extent not commercially available may be synthesized by techniques well known in the synthetic chemical arts. See, e.g., the previously incorporated by reference U.S. Pat. Nos. 5,646,111 and 5,693,611 for preparation of the acyl groups at R4. See also, Collins and Ferrier, xe2x80x9cMonosaccharides: Their Chemistry and Their Roles in Natural Products,xe2x80x9d John Wiley and Sons, New York, N.Y., 1995, and xe2x80x9cMethods in Carbohydrate Chemistryxe2x80x9d, Vol VI, Academic Press, New York, N.Y., 1980 for instruction on preparing compounds of formula III and IV.
For example, compounds of formula IV, and by analogy compounds of formula III, may be prepared as illustrated in Scheme 3 below where R7, R7xe2x80x2, and R7xe2x80x3 are as described above. 
Compounds of formula IV(a), dissolved or suspended in a suitable solvent, may be treated with a source of chloride or bromide ion, to provide the compounds of formula IV. Suitable sources of ion include acetyl chloride, hydrochloric acid, hydrobromic acid, mixtures thereof, and the like. A preferred solvent is the source of ion i.e. a preferred method of performing the reaction is to run it neat. For further instruction on this transformation, see Preparations 8 and 9 below.
Compounds of formula IV(a) where R7 is hydroxy at each occurrence and R7xe2x80x3 is either hydrogen or hydroxymethyl are known as carbohydrates or monosaccharides (sugars). These sugars can be modified by replaning one or more hydroxy groups with hydrogen, azide, or amino to provide the rest of the compounds of formula IV(a). Such compounds may be prepared as illustrated in Scheme 4 below where Lg is an activated hydroxy leaving group. Positions left open for substitution in Scheme 4 are assumed to be hydrogen, azide, protected hydroxy, or protected amino. 
A commercially available compound of formula VI may have its hydroxy group(s) activated for nucleophilic displacement by standard techniques known in the art. For example, the hydroxy group can be sulfonylated with methane-, benzene-, or p-toluene-sulfonyl chloride (or bromide) to provide a compound of formula VII where Lg is OSO2Me, OSO2-phenyl, or OSO2-p-toluenyl. An example of this transformation is illustrated in Preparation 1 below. At this point, the leaving group can be displaced by azide ion, e.g., from sodium or potassium azide as in Preparation 2. Alternatively, the leaving group can be displaced by iodide ion from, e.g., sodium or potassium iodide as in Preparation 3. The resulting compound of formula VIII may be reduced to form a compound of formula IX where one or more of R7, R7xe2x80x2, or R7xe2x80x3 is amino or hydrogen by catalytic hydrogenation or with a reducing agent such as nickel chloride hexahydrate as described in Preparation 4 and Example 41 below. It is preferred that when an amino group is desired in the final product,compound of formula I, that any azido groups be converted to amino groups after coupling to the compound of formula II(a).
The optimal time for performing the reactions of Schemes 1-4 can be determined by monitoring the progress of the reaction by conventional chromatographic techniques. Choice of reaction solvent is generally not critical so long as the solvent employed is inert to the ongoing reaction and sufficiently solubilizes the reactants to afford a medium within which to effect the desired reaction. Unless otherwise indicated, all of the reactions described herein are preferably conducted under an inert atmosphere. A preferred inert atmosphere is nitrogen. Once a reaction is complete, the intermediate compound may be isolated by procedures well-known in the art, for example, the compound may be crystallized or precipitated and then collected by filtration, or the reaction solvent may be removed by extraction, evaporation or decantation. The intermediate compound may be further purified, if desired, by common techniques such as crystallization, precipitation, or chromatography over solid supports such as silica gel, alumina and the like, before carrying out the next step of the reaction scheme.